1. Field of the Invention
The present invention relates generally to an epoxy resin, and more particularly, to a silicone-modified epoxy resin with heat resistance enhanced through condensation polymerization of a methoxy group silicone intermediate to a bisphenol-A or bisphenol-F based epoxy resin, and its method of preparation as well as to a composition comprising the said silicone-modified epoxy resin.
2. Description of the Related Art
The structure of the following formula 1 represents a common bisphenol-A or bisphenol-F based epoxy resin. 
In formula 1, R is xe2x80x94CH3 or H, whereupon R is CH3 for a bisphenol-A based epoxy resin or H for a bisphenol-F based epoxy resin, and n is 1-10.
The bisphenol-A or bisphenol-F based epoxy resin having the formula 1 is of value for use in coatings, electric materials, civil engineering and construction materials and adhesives, in combination with various curing agents of polyamide resins, aromatic polyamines, aliphatic polyamines and anhydrides.
Such an epoxy resin is used for a powder coating composition but is inadequate for use as a coating resin for hot appliances such as ovens due to its poor heat resistance, i.e., it discolors at a high temperature of above 200xc2x0 C.
It is, therefore, an object of the present invention to provide a bisphenol-A or bisphenol-F based epoxy resin with high heat resistance and its method of preparation as well as a composition comprising the epoxy resin.
To achieve the above object, there is provided a method for preparing a silicone-modified epoxy resin according to the present invention which is obtained through condensation polymerization of a methoxy group silicone intermediate to a bisphenol-A or bisphenol-F based epoxy resin.
The structure of the silicone-modified random copolymer epoxy resin according to the present invention is shown in the following formula 2. 
In formula 2, wherein x, y and z are more than 1, and Ep is 
and wherein n is 1-10.
When the weight ratio of the methoxy group silicone intermediate is 20(xc2x11) wt. % based on the total weight of the reactants, the silicone-modified epoxy resin is obtained as an opaque and pale yellow mass having the equivalent weight of 1100 to 1300 g/eq and the fusion viscosity of 1000 to 5000 at 175xc2x0 C.
A description will be made below as to a method for preparing the silicone-modified epoxy resin of the present invention.
First, a common bisphenol-A or bisphenol-F based epoxy resin is heated and melted at 50 to 150xc2x0 C. To the epoxy resin is added 5-50% wt. % of a methoxy group silicone intermediate based on the total weight of the reactant and the mixture is slowly heated at 150xc2x0 C. to 200xc2x0 C. Samples are collected at time intervals of one hour from the time the temperature of the mixture reaches 150xc2x0 C. At a desired fusion viscosity, the mixture is cooled below 150xc2x0 C. to terminate the reaction.
To sum up, the method for preparing the silicone-modified epoxy resin of the present invention includes the steps of: heating and melting the epoxy resin; adding an appropriate amount of the methoxy group silicone intermediate to the melted epoxy resin; and heating the mixture to obtain the product of a desired fusion viscosity.